At most schools, if a child is flailing academically, it is treated as a private matter.

But at Success Academy Harlem 4, one boy’s struggles were there for all to see: On two colored charts in the hallway, where the students’ performance on weekly spelling and math quizzes was tracked, his name was at the bottom, in a red zone denoting that he was below grade level.

The boy, a fourth grader, had been in the red zone for months. His teacher, Kristin Jones, 23, had held meetings with his mother, where the teacher spread out all the weekly class newsletters from the year, in which the charts were reproduced. If he studied, he could pass the spelling quizzes, Ms. Jones said — he just was not trying. But the boy got increasingly frustrated, and some weeks Ms. Jones had to stop herself from looking over his shoulder during the quizzes so she would not become upset by his continued mistakes.

Then, one Friday in December, she peeked at his paper, and a smile spread over her face. After he handed in his quiz, she announced to the class that he had gotten a 90. “I might start crying right now,” she said, only half-joking. “I’ve got to call your mom.”

In its devotion to accountability, Success Academy, New York City’s polarizing charter school network, may have no peer.

Though it serves primarily poor, mostly black and Hispanic students, Success is a testing dynamo, outscoring schools in many wealthy suburbs, let alone their urban counterparts. In New York City last year, 29 percent of public school students passed the state reading tests, and 35 percent passed the math tests. At Success schools, the corresponding percentages were 64 and 94 percent.

Those kinds of numbers have helped Success, led by Eva S. Moskowitz, expand to become the city’s largest network of charter schools, which are publicly funded but privately operated. By next year Ms. Moskowitz, known for her attention-grabbing rallies and skirmishes with the teachers’ union and Mayor Bill de Blasio, will have 43 schools; a proposal by Gov. Andrew M. Cuomo could bring her closer to her goal of 100. That would give Success more schools than Buffalo, the state’s second-largest district.

In a rare look inside the network, including visits to several schools and interviews with dozens of current and former employees, The New York Times chronicled a system driven by the relentless pursuit of better results, one that can be exhilarating for teachers and students who keep up with its demands and agonizing for those who do not.

Rules are explicit and expectations precise. Students must sit with hands clasped and eyes following the speaker; reading passages must be neatly annotated with a main idea.

Incentives are offered, such as candy for good behavior, and Nerf guns and basketballs for high scores on practice tests. For those deemed not trying hard enough, there is “effort academy,” which is part detention, part study hall.

For teachers, who are not unionized and usually just out of college, 11-hour days are the norm, and each one is under constant monitoring, by principals who make frequent visits, and by databases that record quiz scores. Teachers who do well can expect quick promotions, with some becoming principals while still in their 20s. Teachers who struggle can expect coaching or, if that does not help, possible demotion.

Rachel Tuchman, 25, said that during her three years as a teacher at Success, she had friends who worked in the fields of finance and consulting, and she went to work earlier and stayed later than they did.

“You’re being treated like you’re on the trading floor at Goldman while you’re teaching in Harlem,” said Ms. Tuchman, who is now in her first year at Yale Law School.

She also said that she thought the workload was necessary to achieve the results that Success has, adding, “It takes a very specific type of person who can handle the pressure.”

One consequence of the competitive environment is a high rate of teacher turnover. Some teachers who left said that the job was too stressful. Others said they left because they disagreed with the network’s approach, particularly when they believed it was taken to extremes. In an internal email that some former teachers said typified the attitude at some schools, one school leader said that students who were lagging should be made to feel “misery.” Suspension rates at Success schools, compared with public schools, are higher.

Former staff members described students in third grade and above wetting themselves during practice tests, either because teachers did not allow them to go to the restroom, which Ms. Moskowitz disputed, or because the students themselves felt so much pressure that they did not want to lose time on the test.

Jasmine Araujo, 25, who joined Success through the Teach for America program, quit after half a year as a special-education teacher at Success Academy Harlem 3. She now teaches at a charter school in New Orleans. “I would cry almost every night thinking about the way I was treating these kids, and thinking that that’s not the kind of teacher I wanted to be,” Ms. Araujo said.

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Students at Success Academy Harlem North Central work together during a writing exercise.Credit
Nicole Bengiveno/The New York Times

By the Numbers

Ms. Moskowitz and a number of her teachers saw the network’s exacting approach in a different way: as putting their students on the same college track as children in wealthier neighborhoods who had better schools and money for extra help. Success students are generally barred from the city’s best elementary schools because they do not live in those schools’ zones.

“For affluent parents who are concerned about the test scores, they have an exit strategy — their exit strategy is to hire a private tutor,” Ms. Moskowitz said.

No one criticizes those parents, but “when we support our students, we get criticized,” she said.

“And I would argue that it’s not fair that only the kids who can hire private tutors should do well.”

At Success, everyone is measured by whether their students are doing well.

After every networkwide quiz, students’ scores are entered into the Success computer system, which then ranks each teacher. The purpose of this, teachers and principals said, is to identify high performers and to see what practices they are using, and conversely, to determine which teachers might need better practices.

“We’ve never had a conversation where, like, ‘You are 32nd in the network,’ ” said Lisa Sun, the 26-year-old principal at Success Academy Harlem North Central, a middle school. Rather, she said, she discusses with the teacher which skills the students are lacking, as reflected by the data. “ ‘And it’s not because of them, it’s because of you. We have to talk about what you need to fix to make it better.’ ”

A teacher whose students are performing poorly on assessments, or who cannot maintain discipline, might be moved midyear to another grade, an assistant teacher’s position or tutoring outside the classroom. At the beginning of the year, each class is named after the college that its lead teacher graduated from and the students’ expected year of college graduation. Dana Adnopoz’s homeroom at Success Academy Harlem North Central is Dartmouth 2026. Ms. Jones and her co-teacher have Hunter-Siena 2027.

But because teachers frequently leave or move, one teacher who taught at Success Academy Harlem 3 from 2010 to 2012 and left because she viewed it as overly strict recalled that in the spring of her second year, only a few of the classes in the school were still being led by the teacher whose college they were named after.

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A lesson in progress at Success Academy Harlem 4.Credit
Nicole Bengiveno/The New York Times

This teacher, like some other former Success teachers, did not want to be named criticizing the network. These former teachers said they feared hurting their future job prospects by disparaging a former employer or by being identified as critics of charter schools.

Dawn to Dusk

Each school day, Kristin Jones takes a 5:30 a.m. ferry from Staten Island, where she lives with her mother and two younger siblings, to Manhattan. In the winter, the sun is not yet up when she walks into school at 6:40 a.m.

Growing up, Ms. Jones always knew she wanted to be a teacher. She would tape loose-leaf paper to the mirror on her dresser to turn it into a makeshift blackboard and have her cousin and younger brother pretend to be her students.

Beginning teachers at Success are paid comparably with those in city public schools though instead of a pension, they receive contributions to a retirement account. Unlike public-school teachers, who often have to use their own money for basics like photocopies, Ms. Jones and her colleagues do not worry about supplies. The closets teem with notebooks, folders, pencils and pens. Each middle school student receives an iPad. Success Academy schools are also rich in the kind of extracurricular activities that have increasingly been cut from public schools, such as art, music, chess, theater, dance, basketball and swimming.

Success Academy supplements the public money it receives with money raised from private donors. In its 2013 fiscal year, the most recent for which fund-raising figures are publicly available, it received nearly $72 million in public funds and $22 million in donations.

Because so many administrative functions at Success schools are handled by the organization, principals have a lot of time to observe teachers. When William Loskoch, Ms. Jones’s principal, visited her classroom one day in December, he frequently stopped her co-teacher, Sarah Vistocco, 24, who had started at the network in May, to redirect a discussion or ask her to reinforce the rules.

When a student was struggling to come up with an adjective to describe the protagonists of two myths the class had read and Ms. Vistocco moved on, Mr. Loskoch, 34, stopped her and went back to the girl to try to draw her out.

When the students were sitting on the floor and he noticed that they were not sitting properly, he interrupted the lesson and said, “Ms. Vistocco, can you reset your carpet expectations?”

At Success Academy Harlem 4, like other schools in the Success Academy network, educators demand excellence and orderliness from students.Credit
Nicole Bengiveno/The New York Times

Success has stringent rules about behavior, down to how students are supposed to sit in the classroom: their backs straight, and their feet on the floor if they are in a chair or legs crossed if they are sitting on the floor. The rationale is that good posture and not fidgeting make it easier to pay attention. Some teachers who had orderly classrooms and a record of good student performance said, after their first year, their school leaders allowed them to bend the rules somewhat, such as not requiring students to clasp their hands as long as their hands were still.

“We believe that structure and consistency leads to better outcomes,” Ms. Moskowitz said. The network’s rules, she said, were consistent with expectations of students throughout most of the history of American education.

“Maybe some people prefer chaos,” she added. “We don’t.”

Indeed, watching the students at Success Academy Harlem 4 walk to lunch, the scene was anything but chaotic. In their blue and orange uniforms — the girls wear jumpers, and the boys shirts and ties — they walked silently in two lines, starting and stopping at the teacher’s command. If so many children walking in formation was reminiscent of the von Trapp children at the beginning of “The Sound of Music,” the orderliness also meant that no time was wasted.

Likewise, inside Ms. Jones’s classroom, the atmosphere was calm, and she was demanding.

When the students were writing summaries of myths, she scolded the class: “I don’t want to continue seeing names of characters that start with lowercase letters. It’s an indicator of low effort.”

But when she was pleased with a student — as when the boy scored well on his spelling quiz — she radiated pride.

Asked whether she thought the students who were in the red zone would be demoralized, Ms. Jones said, “I’m sure they’re not happy about it.”

“But they’re very resilient,” she added. “And then, as soon as they get a great grade, they’re praised for it,” and, she said, they can see the difference that their increased effort made.

“They don’t want to stay there,” she said. “They want to improve.”

Carrots and Sticks

In 2005, Ms. Moskowitz, then a city councilwoman, ran for Manhattan borough president and lost — in part because of opposition from the teachers’ union, the United Federation of Teachers, which was enraged by a series of hearings she held in the City Council that were critical of work rules embedded in the union’s contract.

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Students’ weekly quiz scores are posted in charts in the hall.Credit
Nicole Bengiveno/The New York Times

After the election, she was recruited by a pair of hedge fund managers who were interested in setting up a charter school, and she opened the network’s first, the Harlem Success Academy, in 2006. In subsequent years she opened more schools, first in Harlem and then in other neighborhoods in the city, and now has a total of 9,000 students in schools in every borough but Staten Island.

The Bloomberg administration gave her free space in public schools, often angering parents and teachers in the schools that had to share buildings with Success. Last year, after Mr. de Blasio briefly blocked three Success schools from public space and threatened to charge the network rent, Mr. Cuomo pushed through a law guaranteeing all new or expanding charter schools in the city free space or money to find their own.

Ms. Moskowitz has used her high test scores to argue that she should be allowed to open more schools, and an effort by Mr. Cuomo to raise the limit on the number of charter schools in the state could make it easier for her to do so.

At any given time, multiple carrots and sticks are used in the quest to make sure every student does well on the standardized tests. This system goes into overdrive in late January, as the annual exams, which begin this year on April 14, approach.

Success did not allow a reporter to observe test preparations, but teachers and students described a regimen that can sometimes be grueling.

To prepare for the reading tests, students spend up to 90 minutes each day working on “Close Reading Mastery” exercises, consisting of passages followed by multiple-choice questions. The last two Saturdays before the exams, students are required to go to school for practice tests.

Students who do well on practice tests can win prizes, such as remote-controlled cars, arts and crafts kits, and board games. Former teachers said that they were instructed to keep the prizes displayed in the front of their classroom to keep students motivated.

Students who are judged to not be trying hard enough are assigned to “effort academy.” While they redo their work, their classmates are getting a reward — like playing dodge ball against the teachers, throwing pies in the face of the principal or running through the hallways while the students in the lower grades cheer.

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Eva S. Moskowitz, the founder and chief executive of Success Academy charter schools.Credit
Jake Naughton for The New York Times

On the Friday before test preparations began, a calendar counting down the days to the test hung on the wall in Yale 2025, a sixth-grade classroom at Success Academy Harlem North West. The page for Monday was already displayed; in large type, it said: “53 days left.”

Carolyn Farnham, 24, the teacher, asked her students how they felt about the start of test preparations.

“It has the potential to be both really, really dull and really, really stressful,” she said to her students, adding, “That’s certainly not what I want.”

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Some students responded that they did not mind because they had done well on the tests in the past. But several said they disliked it.

“I know that it’s here to help us,” one girl, Maliha, said. “But sometimes when people don’t get the best score, they seem to feel, like, really down on themselves. And when effort academy and detention and stuff like that is introduced,” she said, “one gets — me personally — really angry and upset.”

“I always get a high three or a low three or sometimes a four,” said the boy, Erick. (A three is considered passing, and a four is the highest score.) “What I don’t like is I have to go to school on Saturdays, so I feel like I don’t get rest, and I get a lot of stress in my neck because I got to go like this all the time,” he said, hunching forward like he was looking at a test paper.

Another girl, Ruqayyah, agreed that test preparations caused anxiety. But “on the other hand, there’s prizes,” she said, “which are really cool and motivate us to do our best.”

“I hope also you want to do your best for you,” Ms. Farnham said, “not just for prizes.”

The network’s critics — including the teachers’ union, which sees Success as taking money and space from public schools — say the network’s high scores are a mirage created, in part, by inordinate test preparation.

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Recess at Harlem 4.Credit
Nicole Bengiveno/The New York Times

The network’s oldest students are still in high school, so it is difficult to gauge the long-term benefits of their education. Halley Potter, a fellow at the Century Foundation, a progressive policy organization, and the co-author of two books about charter schools, said that network’s test scores were impressive, but that the conclusions that could be drawn from them were limited.

“Success Academy’s strong test scores tell us that they have a strong model for producing good test scores,” Ms. Potter said, adding that there could be lessons in Success’s practices for schools that are trying to improve their scores.

She noted that Success schools tend to have fewer nonnative English speakers and special-education students than public schools; those groups tend to score lower on tests. Ms. Potter also said that the network has made trade-offs, including not offering foreign languages until eighth grade, in order to devote more time to math, English and science, the only subjects in which all elementary and middle school students take state tests.

Teachers and principals at Success said that they prepare their students so intensely for the tests because of the opportunities that high scores can present, such as invitations to top public middle or high schools, or scholarships for private schools.

Two documentaries, “Waiting for Superman” and “The Lottery,” have captured the desperation of parents trying to get their children into Success through the annual lotteries it holds; this year, the network said, it received more than 22,000 applications for 2,688 seats.

Shakeya Matthew’s sons attended Public School 165, on West 109th Street, before getting into Success Academy Harlem 4 this year. Ms. Matthew, 33, said that her younger son had struggled last year in kindergarten and that his teacher seemed overwhelmed. Now, as a Success first grader, he is reading at a second-grade level. She said that she is in more frequent contact with her sons’ teachers now than when her sons were in the public school. Success teachers will call or send her a text during the day or in the evening with news about how one of her sons did on a test or with other updates.

The high-pressure atmosphere at Success leads to substantial teacher turnover, though the precise rate is unclear. According to the latest school report cards, in 2013-14 three Success schools had turnover rates above 50 percent, meaning more than half the teachers from the previous year did not stay.

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Students from Success Academy Williamsburg at a Families for Excellent Schools rally in October.Credit
Karsten Moran for The New York Times

But Success officials said that these figures were inflated by the number of teachers who move from one Success school to another, or to nonteaching positions within the network. According to its own numbers, attrition from the network from June 2013 to June 2014 was 17 percent. By comparison, attrition from the city’s public school system in 2013-14 was 6.1 percent, according to the Education Department.

Still, current and former employees said departures were common.

Ariadna Phillips-Santos, 34, taught kindergarten and first and second grades at Success Academy Harlem 5 from 2010 until 2012. Having worked in public schools, she was impressed by the academic rigor and the plentiful supplies. But she was raising a young son on her own, and juggling his care with her long work hours was almost impossible, she said. Ms. Phillips-Santos, who is now a dean at a public elementary and middle school in the Bronx, said she recalled asking her Success principal one day if she could leave at 4:55 p.m. — after the students had been dismissed — because her son’s day care had called saying that he had a fever and was vomiting, and being told, “It’s not 5 o’clock yet.”

Ms. Moskowitz said that Success was accommodating to working parents. She said that Success allowed some teachers and even some principals to work part time and that the network offers a month of paid maternity and paternity leave.

Most of the former teachers interviewed, however, said that they left not because of the workload, but because they disagreed with Success’s approach, which they found punitive.

One teacher complained that she was expected to announce all of her students’ scores on practice tests, by asking those who had scored a four to stand up, followed by those with a three and then those with a two. The teacher and her colleagues persuaded their supervisors not to make students with a score of one stand up, but those students were still left conspicuously sitting down, she said.

At one point, her leadership resident — what the network calls assistant principals — criticized her for not responding strongly enough when a student made a mistake. The leadership resident told her that she should have taken the student’s paper and ripped it up in front of her. Students were not supposed to go to the restroom during practice tests, she said, and she heard a leader from another school praise the dedication of a child who had wet his pants rather than take a break.

“I dreaded going into work,” the teacher, who now teaches in a public school, said.

Other former staff members also described students having wet themselves, in some cases during practice tests. Two former staff members who worked at Success Academy Harlem West, a middle school, in the 2013-14 school year, said that they recalled having to go to the supply closet to get extra underwear and sweatpants, which were always on hand, for students who had wet themselves.

Ms. Moskowitz said that, to mimic the environment of the actual test, when students are not supposed to go to the restroom except for an emergency, Success has all students go to the restroom immediately before practice tests. But students are still allowed to go during tests, she said. She acknowledged that there were sometimes accidents, but attributed them to the challenges of sharing space in public school buildings, which meant the restrooms were sometimes several floors away.

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Ms. Moskowitz in a classroom at Harlem Success Academy 3 in 2008.Credit
James Estrin/The New York Times

“We have plenty of kids who don’t always prepare adequately,” Ms. Moskowitz said, adding that “very occasionally there are accidents, and we get that it’s uncomfortable for the student.”

“It’s very emotional,” she said. “Teachers get emotional about it.”

Suspension Rates

Several former teachers and staff members said that they had also been uncomfortable with Success’s suspension rates.

At Success Academy Harlem 1, as the original school is now called, 23 percent of the 896 students were suspended for at least one day in 2012-13, the last year for which the state has data. At Public School 149, a school in the same building, 3 percent of students were suspended during that same period. Statewide, the average suspension rate is 4 percent. (A spokeswoman for Success said that the suspension rate at Success Academy Harlem 1 has since declined to 14 percent, and that several of the newer schools had rates below 10 percent.)

Students who frequently got in trouble sometimes left the network, former staff members said, because their parents got frustrated with the repeated suspensions or with being called in constantly to sit with their children at school.

Ms. Moskowitz said that the question of what was an appropriate number of suspensions was a complicated one, but that the suspension rate in public schools should not be regarded as “the gold standard.” She said that even very young children could do things that required an intervention, such as bringing razor blades to school or cursing at teachers.

“Often the suspensions are really to get the parents and the school to be on the same team, that there’s a serious issue,” she said. “If we don’t intervene, when they’re 13, that’s going to be a bigger problem,” she said.

The network’s critics say that its performance is skewed by the departure of its most difficult students. In a visit last month to a public school where 4 percent of students passed last year’s math tests, and that shares a building with a Success school where 96 percent of the students passed, the city’s schools chancellor, Carmen Fariña, said, “We would like to be at that percentage, but we keep all our kids from the day they walk into the building.”

Success students who leave after fourth grade are not replaced because, Ms. Moskowitz said, new students entering at that point would be too far behind their classmates. But even if all those students stayed and continued to do poorly, Success schools would still significantly outperform their neighboring schools on tests.

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At the start of a quiz and when a buzzer sounds at the end, students are instructed to raise their pencils at Success Academy Harlem 4.Credit
Nicole Bengiveno/The New York Times

Dahlia Graham, a teacher who came to Success Academy Harlem 1 in 2009, said that in the public school in Bedford-Stuyvesant, Brooklyn, where she previously taught, there was no clear discipline system. If a student hit another student, he might be removed from class briefly, but then would return, still angry, and disrupt the class again. She said it was a relief when she got to Success, where she said hitting resulted in suspension.

“It made my life so much easier,” Ms. Graham said.

As for the teachers who said they did not like the environment, Ms. Moskowitz said: “Most of the people who leave are a little angry, like they don’t like their work and they don’t seem happy teaching, and we really can’t have people who don’t love it.”

A Demanding Culture

On April 1, 2012, a leadership resident at Success Academy Harlem 2, Lauren Jonas, sent an email to her fourth-grade teachers.

The email, provided by a former staff member, said that the results on a recent, three-day practice test were “not what we had hoped for.”

“You must demand every single minute,” Ms. Jonas wrote. “You must have higher behavioral and academic expectations than ever before.” Every letter was capitalized.

Nine to 12 students had failed to use the test-taking strategies they had been taught, known as the “plan of attack,” Ms. Jonas wrote.

“We can NOT let up on them,” she continued. “Any scholar who is not using the plan of attack will go to effort academy, have their parent called, and will miss electives. This is serious business, and there has to be misery felt for the kids who are not doing what is expected of them.”

At Ms. Jonas’s school, 64 percent of the teachers the year she wrote that email were not teaching there the next year, according to state figures. Researchers have linked high teacher turnover to lower performance by students on tests, but that is not the case at Success. At Success Academy Harlem 2 last year, 91 percent of students passed the state math tests, up from 76 percent the previous year. At Public School 30, which shares the building with Success Academy Harlem 2, 16 percent of students passed.

Ms. Jonas is now principal of one of the network’s newest schools, Success Academy Harlem North West, a middle school.

When the 2012 email was read to her recently, Ms. Jonas cringed and said that she did not remember writing it. She said that she did not want students to be miserable and described her words as “poorly chosen.”

“I should be certainly more careful in how I’m communicating and how others might misinterpret the meaning behind it,” she said.

But Ms. Moskowitz defended the wording of Ms. Jonas’s email, saying that a reporter was reading too much into it.

“We use that terminology sometimes, meaning, you know, ‘Kids, you got to get it right the first time, and we’re not playing,’ ” she said.

“That is part of our culture — not having kids getting away with just not trying,” she continued. “Everybody’s working too hard. Parents are sacrificing to get up early. Teachers are working really hard. Simply not trying is not part of our culture.”

Are you a former or current Success Academy parent or student who would like to share your experience? The Times would like to hear your story. Please write to us at cityroom@nytimes.com. Your information will be kept confidential. A reporter or editor may follow up with you.

A version of this article appears in print on April 7, 2015, on Page A1 of the New York edition with the headline: At Charters, High Scores and Polarizing Tactics . Order Reprints|Today's Paper|Subscribe